In the oil preservation type system, a synthetic rubber bladder, is stretched over the surface of the oil in a conservator tank to completely isolate the insulating oil from outside air. The bladder shape varies according to expansion and contraction of the oil, maintaining pressure in the bladder at atmospheric pressure. Since the bladder completely isolates the oil from the atmosphere, absent a failure of the bladder, there is no possibility for oxygen or moisture penetrating the oil. Accumulation of water in a conservator tank can contaminate the oil or can even cause confusion with respect to the oil level indication if one believes the bladder is operating properly.
Since the conservator tanks are sealed, it is difficult to access the inside of the tank to ensure that the bladder is functioning properly to isolate the oil from the air. Thus, there is a need to provide a sensor associated with the bladder to detect the presence of any moisture or oil on top of the bladder inside of the conservator tank.